Conventionally, as disclosed in Japanese Patent Laying-Open Nos. 2005-174844, 2005-174691 and 9-199177, various types of stacked secondary batteries, which are formed by stacking a plurality of unit secondary battery cells and mounted as a motor driving source of an electric vehicle (EV) or a hybrid vehicle (HEV), have been proposed. A unit secondary battery cell includes an electrolyte layer, a cathode layer formed on one surface of the electrolyte layer, an anode layer formed on the other surface of the electrolyte layer, and collectors formed on surfaces of the cathode layer and anode layer.
By way of example, a stacked secondary battery described in Japanese Patent Laying-Open No. 2005-174844 is formed by stacking a plurality of unit secondary battery cells, and it includes a positive collector plate on one end surface and a negative collector plate on the other end surface in the direction of stacking the unit secondary battery cells.
A positive electrode tab or a negative electrode tab for taking out current is provided on the positive collector plate and the negative collector plate.
The current flowing through the positive collector plate and negative collector plate provided in unit secondary battery cell and stacked secondary battery concentrates to a path having the smallest electric resistance to the positive electrode tab or negative electrode tab. Therefore, at a portion where the path having the smallest electric resistance of the positive collector plate and the negative collector plate is positioned, temperature increases.
When temperature increases at a part of the negative collector plate and the positive collector plate, electrode reaction is activated at a part of unit secondary battery cells adjacent to the negative collector plate and the positive collector plate, and that part would be locally degraded.